Fesoterodine is an antimuscarinic for the treatment of overactive bladder syndrome. Treatment with fesoterodine has substantially improved the symptoms of overactive bladder syndrome which patients find extremely stressful. In all clinically relevant outcomes from both phase III studies (2, 3) (urge incontinence results/24 h, micturition frequency, median micturition volume), statistically significant improvements were obtained over placebo. Fesoterodine is currently marketed under the brand name Toviaz®. Fesoterodine is a prodrug. Taken orally, the prodrug is activated by esterases in the human body to the active metabolite.
The IUPAC name for fesoterodine [INN] is 2-[(1R)-3-(diisopropylamino)-1-phenylpropyl]-4-(hydroxymethyl)phenyl-isobutyrate. The chemical structure of fesoterodine is illustrated in formula (1) below:

Synthesis pathways for fesoterodine can be obtained from EP 1 077 912 B1. Fesoterodine salts are described in EP 1 230 209 B1.
Fesoterodine is not particularly stable to hydrolysis. For this reason, fesoterodine tablet formulations were proposed in WO 2007/141298 which contain fesoterodine in the form of a fumarate or hydrogen fumarate salt and a stabilizer against hydrolysis; the stabilizer is preferably xylitol. However, the use of xylitol in pharmaceutical formulations is usually undesirable. In addition, it has been shown that despite using xylitol, processing the corresponding pharmaceutical formulations is problematic because of hygroscopic properties. In addition, the resulting dosage forms cause problems linked to stability on storage; as an example, they can only be packaged in expensive films with low water vapour permeability.